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NIR-10
Noise / Interference
Reduction Unit
Instruction Manual
Revision 3.4 - July 1996
Publication # 5900-700200
JPS Communications, Inc.
CONTENTS
SECTION 1
BRIEF DESCRIPTION .................................................................. 1
Noise Reduction Mode .................................................................. 1
Notch Filter Mode .......................................................................... 1
Peak Mode ...................................................................................... 2
Bandpass Mode .............................................................................. 3
Bypass Mode .................................................................................. 3
SECTION 2
QUICK OPERATION .................................................................... 4
Connect Power ............................................................................... 4
Connect Audio Input ...................................................................... 4
Connect Speaker or Headphones ................................................... 4
Turn on Power ................................................................................ 5
Initial Settings ................................................................................. 5
Radio Settings ................................................................................ 5
NIR Mode ...................................................................................... 5
Bandpass Mode .............................................................................. 6
Notch Mode ................................................................................... 6
Peak Switch .................................................................................... 6
SECTION 3
CONNECTIONS ............................................................................ 8
Power Requirements ...................................................................... 8
Vehicular Operation ....................................................................... 8
Audio Input .................................................................................... 8
Input Level Adjust ....................................................................... 10
SECTION 3 (Cont.)
Speaker Output ............................................................................. 10
Headphone Output ....................................................................... 10
Remote Bypass ............................................................................ 11
Inv Remote Bypass ...................................................................... 12
SECTION 4
CONTROLS & INDICATORS .................................................... 13
Power Switch & Indicator ............................................................ 13
Mode Switch ............................................................................... 13
BW (Function) Switch ................................................................. 13
NIR Level / BP Shift Control ....................................................... 14
Peak Indicator ............................................................................... 14
Volume Control ........................................................................... 14
SECTION 5
OPERATION ............................................................................... 15
NIR/NF Mode on Voice ............................................................... 15
PEAK Mode on Voice ................................................................. 19
NIR/PEAK Mode on Static Crashes ............................................ 20
NIR Mode on CW ........................................................................ 20
NIR Mode on RTTY, etc. ............................................................. 21
PEAK Mode on CW/DATA ........................................................ 21
BANDPASS Mode ....................................................................... 21
BANDPASS Mode on Voice ....................................................... 22
Operational Limitations ................................................................ 22
Transmit Audio Processing .......................................................... 24
SECTION 6
TECHNICAL INFORMATION ................................................... 25
Specification ................................................................................. 25
Troubleshooting ........................................................................... 27
Remote Bypass Connections ....................................................... 28
Audio Section Technical Description ........................................... 30
DSP Section Technical Description .............................................. 31
FIGURES
FIGURE 1
Connection Diagram ...................................................................... 7
FIGURE 2
Audio/Power Supply Section Schematic ...................................... 34
FIGURE 3
DSP Section Schematic ................................................................ 35
FIGURE 4
Connections for Transmit Audio Processing ................................ 36
TABLES
TABLE 1
Selection of Operating Modes by Mode and BW Switch
Position .................................................................................... 16
SECTION 1
BRIEF
DESCRIPTION
NOISE REDUCTION
MODE (NIR)
NOTCH FILTER
MODE
The NIR-10 is an audio processor designed to enhance the quality of
received voice and CW transmissions. Its modes of operation are explained
below. Basically, the unit takes audio from a receiver or transceiver,
processes it, then feeds it to an external speaker or headphones for
listening. It does this processing using a powerful 40 MHz Digital Signal
Processor (DSP) for the filtering, noise reduction, and heterodyne removal.
The technical information section explains how the DSP works.
The Noise and Interference Reduction (Spectral Subtraction) mode
automatically enhances speech by recognizing the characteristics of
human vocal cord physics and the subsequent relationships of speech
frequencies relative to frequencies of non-speech. The speech frequencies
are then allowed to pass, while non-speech frequencies may be reduced
by using a front panel control. In this mode, which is language and male/
female voice independent, the NIR-10 removes noise and heterodynes
occurring in the presence of speech without reducing the audio bandwidth
and with minimal corruption of the speech itself. The amount of noise
reduction is continuously variable from zero to maximum by means of
the NIR LEVEL control on the front panel. As long as the NIR LEVEL
control is not advanced so far as to overprocess the signal, the NIR mode
will also effectively remove noise from CW and data signals as well as
voice.
The Notch Filter (NF) mode provides cancellation of tones from tuneups, heterodynes, CW, RTTY, or similar signals without interfering with
voice signals. Unlike conventional notch filters, this mode easily removes
multiple tones. The NF mode is made operational by placing the BW
1
(FUNCTION) switch in the WIDE/NF position while the MODE switch
is in either BYPASS or NIR position. See Table I. When energized, this
mode automatically removes offending tones regardless of the position
of the NIR control. The NF mode is disabled by placing the BW switch
in NARROW (lower) position. NF doesn’t function in the BANDPASS
filter mode. The NOTCH mode operates in “real time”, so there is no
processing delay.
PEAK MODE
The PEAK (Dynamic Peaking) mode is useful for reducing white or pink
noise (atmospheric) and other similar noise types from audio. It can be
used alone or in conjunction with the NIR mode. PEAK mode provides
dynamic bandpass filters around all coherent frequencies (voice, CW,
data, etc.) within the audio passband. It rejects the non-coherent
frequencies of white noise and similar noise types. This provides a
second means of noise reduction for the user. With CW signals, if a CW
tone can be separated with the receiver filter, it can be further peaked and
noise-reduced using the PEAK function.
The PEAK mode is made operational in either BYPASS or NIR modes
by placing the BW (FUNCTION) switch in the MED/PK position. The
PEAK function is disabled by placing the BW switch in the NARROW
(lower) position. So the PEAK mode may be used by itself (MODE in
BYPASS) or along with the NIR mode. In some cases, the PEAK
function will be most effective, or the NIR mode will best remove the
unwanted interference, and there will be occasions where the PEAK and
NIR modes together are required to eliminate the noise satisfactorily.
The PEAK mode does not function in the BANDPASS filter mode. The
2
PEAK mode operates in “real time”, so there is no processing delay in
this mode.
NOTE
When using the PEAK function on weak signals, the output
audio level MAY decrease. So it may be necessary to increase
the audio input from the receiver to obtain an adequate listening
level. Observe the PEAK LED to be sure that the NIR-10 is not
being overdriven. There may also be times when the PEAK
function will be most effective at reduction of the noise by
REDUCING the audio input from the receiver and increasing
the NIR VOLUME to restore the proper listening level.
BANDPASS MODE
BANDPASS mode is intended to enhance CW, RTTY, and voice reception
when adjacent channel interference is present; the unit operates as a
super-selective digital audio filter with three switch-selectable bandwidths.
The filter center frequency may be shifted anywhere in the 300 to 3400 Hz
audio range by means of the BP SHIFT control on the front panel. Noise
reduction is not usable in conjunction with the BANDPASS filter mode.
Other bandwidths are available from the factory on special order.
BYPASS MODE
The DSP audio processing requires some input to output signal delay.
Although unimportant when receiving, this delay is objectionable when
monitoring your own transmission through the NIR-10 Therefore, a
BYPASS mode has been provided to remove all processing and delay
from the NIR-10 output. BYPASS may be enabled from your transmitter’s
key line as well as from the front panel.
3
SECTION 2
QUICK
OPERATION
This section lets you get on the air with the NIR-10 as quickly and as
simply as possible. Refer to the connection diagram on page 4. See the
following sections of this manual for more detailed operation and
connection information.
CONNECT POWER
The NIR-10 operates from a nominal +12 VDC power source. Plug an
AC to 12VDC Adapter into the NIR-10’s DC IN (J1) jack on the rear
panel. Although the electronics are protected for reverse polarity,
damage to the printed circuit tracks may result if the correct polarity is
not observed. If you solder on your own power plug, be sure to check
for the correct polarity - center terminal is positive. An adapter with 1
Amp output current capability is required. The NIR-10 DC IN jack is a
coaxial type, 2.5mm ID, 5.0 or 5.5mm OD, center positive (Radio Shack
274-1568 or 274-1573).
CONNECT AUDIO
INPUT
Connect the Speaker Output of your receiver or transceiver to the
AUDIO INPUT (J3) jack. The NIR-10 AUDIO INPUT jack is an RCA
Phono type - it is NOT a 1/8" phone jack.
CONNECT SPEAKER
or HEADPHONES
Connect a 3.2Ω or greater speaker to the SPEAKER OUTPUT (J2), or
plug your headphones into the front panel PHONES jack. The NIR-10
SPEAKER OUTPUT jack is an RCA Phono type - it is NOT a 1/8" phono
jack.
4
TURN ON POWER
Now turn on the NIR-10’s POWER switch. The LED next to the switch
should light. If it doesn’t, check your power source and connections.
The red PEAK LED next to the VOLUME control should blink three
times (long, short, short), indicating that the unit successfully self-tested.
INITIAL SETTINGS
Put the MODE and BW switches all the way down to BYPASS and
NARROW positions respectively, and set the NIR LEVEL control fully
counter-clockwise to the MIN position. Adjust the VOLUME control to
about mid-range.
RADIO SETTINGS
Turn on your receiver or transceiver and tune in a STRONG voice station.
Adjust your radio’s volume control so that the PEAK LED on the NIR10 flashes occasionally on voice peaks- this sets the proper audio input
level to the NIR-10. Leave your radio’s volume at this setting and then
adjust your listening level only with the NIR-10’s volume control. Turn
off your radio’s speaker so that you are listening to output from the NIR10 only.
NIR MODE
Adjust the NIR-10 VOLUME to a comfortable level. Since the NIR-10
is in the BYPASS mode, you are now listening to unprocessed audio
from your receiver. Now switch the MODE switch up to the NIR position
and experiment with the setting of the NIR LEVEL control. Notice how
the noise melts away as the NIR LEVEL control is advanced. The normal
setting for this control is between 10 and 12 o’clock. Experiment with
CW signals in the NIR mode as this mode is also effective on most CW
signals. (However, the NIR-10 may think that slow CW is an interfering
signal and remove it.)
5
BANDPASS MODE
Now put the MODE switch in the center BANDPASS position. Put the
BW (Bandwidth) switch in the WIDE position. Adjust the BP SHIFT
control back and forth to observe its effect (it’s the same control as
before; the function has now changed). Tune into a crowded part of the
CW band. Narrow the bandwidth using the BW switch. Adjust the BP
SHIFT control and notice how you can use it to pick out individual CW
signals.
NOTCH MODE
Place the MODE SWITCH in BYPASS position. Tune in a strong tone
or heterodyne. Place the BW switch all the way up to WIDE/NF. This
engages the NOTCH FILTER. The carrier should disappear immediately.
PEAK MODE
Now place the BW switch in the middle MED/PK position. This engages
the PEAK FILTER. The tone should now be peaked and the surrounding
noise suppressed. Check this function with voice signals to get familiar
with its noise reducing capabilities. Also try the PEAK and NIR modes
combined for noise reduction. Remember that the degree of cancellation
of noise in the NIR mode is continually adjustable with the NIR LEVEL
control.
6
FIGURE 1 Connection Diagram
7
SECTION 3
This section gives detailed information regarding the connections to the
NIR-10. The unit is very simple to connect and use, but for best results,
follow the guidelines below.
CONNECTIONS
POWER
REQUIREMENTS
VEHICULAR
OPERATION
AUDIO INPUT
8
The NIR-10 operates from +11 to +16VDC. Audio peaks push current
consumption to 1 Amp peak, so an adapter of 1 A capability is required.
If you haven’t bought our adapter (it’s a 1 Amp unit), we recommend
the Radio Shack P/N 273-1653 Adapter. Of course, you may also
operate the NIR-10 from your radio’s auxiliary power or other highquality +12V source. The mating connector is Radio Shack P/N 2741568 or 274-1573.
The NIR-10 may be operated directly from the power system of any
12V negative ground vehicle.
The NIR-10 may be connected to the speaker, headphone, or audio line
outputs of almost any kind of receiver or transceiver. Its audio input is
AC coupled, with an impedance of 22Ω. The input impedance may be
easily adjusted to a high (47kΩ) impedance (see note below), which
means that it may be connected to almost any type of audio output
without causing any loading or other adverse effects. The input is
protected against overloads of up to +50 V.
The front panel PEAK LED makes setting the input level easy: simply
advance your radio’s volume or audio level control until the PEAK LED
flashes occasionally on voice peaks.
NOTE
Some receiver speaker driver amplifiers became unstable when
driving earlier versions of the NIR-10. Symptoms of instability
included rectification or pickup of transmitted RF which then
appeared (possibly distorted and/or at a low level) at the NIR10’s speaker output. This instability has been remedied by
loading the receiver’s speaker output by inserting a 22Ω resistor,
R5, between the NIR-10’s audio input and ground. This resistor
is not required in most cases, and can be clipped out if a high
impedance audio input is required. The resistor is either soldered
directly to the input connector, J3, or is installed on the board
near J3.
NOTE
For best operation and maximum dynamic range, the NIR-10
should have a relatively constant input audio level. This means
that once set, the volume into the unit should be left alone, and
your listening level should be adjusted with the VOLUME
control on the NIR-10. Also, overdriving the input will not result
in improved performance, but will just cause increased audio
9
distortion. The unit is being overdriven if the PEAK LED is on
more than just an occasional flash.
INPUT LEVEL
ADJUST
As shipped from the factory, the gain of the NIR-10 is set for use with
most speaker or headphone outputs when they are adjusted for normal
listening levels. In an unusual installation, more gain may be needed to
boost the input signal level to fully utilize the NIR-10’s dynamic range.
The NIR-10 has an internal jumper which may be changed to raise its
gain when the input signal level is low. This jumper is located on the left
edge of the NIR-10 PC board and is accessible with the cover removed.
Normal signal level is with the jumper in position 1-2; the low level
setting is position 2-3. Make sure that the use of this low level setting is
really needed and that its use doesn’t result in input overload (the PEAK
LED will tell you if it’s overloaded).
SPEAKER OUTPUT
The speaker output is the main audio output from the unit. It can furnish
more than 2W into a 3.2Ω speaker, less into higher impedances. It is also
a general-purpose output intended to drive any type input. It can’t be
harmed by an open or short circuit.
HEADPHONE
OUTPUT
This output is a stereo phone jack connected to the speaker output
through a resistive divider to prevent headphone overdrive. It will
satisfactorily drive 8Ω and higher impedance phones.
10
NOTE
A mono phone plug inserted all the way into the stereo jack will
short both channels and you will get no audio (no damage will
occur, however). A mono plug may be used by inserting it only
to the first detent (about 1/4" from fully seated in the jack). If
you prefer not to do this, a stereo-to-mono adapter is available
from Radio Shack.
REMOTE BYPASS
The sophisticated signal processing done in the NIR-10 requires a certain
amount of audio delay. This delay, on the order of 1/8 second, is
unimportant in receive, but makes transmit signal monitoring through the
NIR-10 all but impossible. For this reason, a BYPASS mode, which
removes all processing and delay, is included in the NIR-10. The
REMOTE BYPASS input allows this mode to be entered via an external
control signal, regardless of the MODE switch position. By connecting
this input to your transceiver’s PTT line or other transmit signal, the NIR10 will be bypassed automatically when you transmit, allowing you to
monitor your own voice or CW transmission through the NIR-10 without
annoying audio delay.
This input forces BYPASS MODE while driven to a voltage of +3V or
higher. It has a 10kΩ impedance and is protected to +50V input.
11
INVERT REMOTE
BYPASS
This input functions the same as the REMOTE BYPASS input except
that it requires the opposite polarity signal. This input requires a ground
or less than +2V to activate. It has a 10kΩ input impedance and is
protected to +50V input.
The two remote bypass inputs are provided to accommodate virtually
any transmitter or transceiver. Section 6 gives further details on
connections to your transceiver.
12
SECTION 4
This section explains the operation of each of the NIR-10 controls.
CONTROLS &
INDICATORS
POWER SWITCH
The POWER switch controls the main power to the unit and the indicator
next to it glows when power is applied.
MODE SWITCH
The MODE switch determines the operating mode of the NIR-10. When
in NIR position, the Noise and Interference Reduction mode is active and
the NIR LEVEL control sets the amount of reduction. When the MODE
switch is in BANDPASS position, the filter mode is active, with the
bandwidth set by the BW switch and the center frequency set by the BP
SHIFT control. In BYPASS position, all delay and processing except for
the notch filter and peak function are removed. BYPASS may be forced
via the remote bypass inputs regardless of the position of this MODE
switch.
BW (FUNCTION)
SWITCH
This switch sets the filter bandwidth only in BANDPASS mode. It has
no effect on audio bandwidth in BYPASS or NIR modes. In BYPASS or
NIR modes, this switch is used to engage the NOTCH or PEAK functions.
The middle position of the switch (MED/PK) engages the PEAK function,
while the upper position of the switch (WIDE/NF) engages the NOTCH
filter. To turn off both functions, place this switch in the lower (NARROW)
position.
13
NIR LEVEL/BP SHIFT
CONTROL
The NIR LEVEL/BP SHIFT control has two functions, depending on
the position of the MODE switch. When in NIR mode, this control is the
NIR LEVEL, setting the amount of noise reduction. The normal setting
for this control is between 10 and 12 o’clock. Settings above 12 o’clock
may be useful for removing interference from strong signals, while fully
counterclockwise gives minimum noise reduction.
When in BANDPASS mode, this control is the BP (Bandpass) SHIFT
control, setting the operating frequency of the filter. The upper frequency
of the bandpass is the reference for this control. The fully counterclockwise
position puts the upper edge of the bandpass at the low end of the audio
range, near 300 Hz, while fully clockwise puts the upper edge of the
bandpass at the high end, near 3400 Hz.
PEAK INDICATOR
The PEAK indicator flashes when the input audio amplitude reaches a
level that is somewhat below the maximum signal that the NIR-10 can
handle without producing distortion. Using this indicator as a guide, the
input audio level may be adjusted to take advantage of maximum
dynamic range, yet avoid overload. The proper input audio setting is that
which causes the PEAK indicator to flash occasionally on voice peaks.
If the PEAK indicator is on continuously, the input audio level is too
high, and should be reduced to avoid distortion. (This indicator also
flashes on power-up during the self-test.)
VOLUME CONTROL
The VOLUME control sets the NIR-10 output audio level at the speaker
and phones outputs.
14
SECTION 5
This section describes the operating procedure using the NIR-10’s
various modes with different types of signals.
OPERATION
NIR/NF MODE on
VOICE
The NIR mode is designed primarily to remove noise occurring in the
presence of speech. It does this by examining the input audio, looking for
signals with speech characteristics, and reducing everything else. Since
the signal and noise levels vary so much on the amateur bands, the NIR10 allows control of the noise reduction level so the performance may be
tailored to the conditions at hand.
With the NIR LEVEL control set fully counter-clockwise, tune your
receiver to a noisy sideband signal. Then adjust the NIR LEVEL control
clockwise and notice how the noise is reduced. Also note that if the noise
level is very high, it is possible to put in too much noise reduction,
reducing speech intelligibility.
Certain types of noise may contain some characteristics of speech,
making them difficult to suppress completely. If you find a noise type
only partially suppressed, try reducing the audio level going into the NIR10. It should be noted that the NIR-10 cannot recover intelligibility of a
voice signal which is grossly corrupted by noise. For signal-to-noise
ratios of 0 dB or better, the unit does an exceptional job of eliminating
noise from speech. It can’t, however, make an S2 voice signal fully
15
TABLE 1
Selection of Operating Modes By Mode and BW Switch Position
16
TABLE 1
(Continued)
17
TABLE 1
(Continued)
18
readable in an S5 noise level. Heterodynes may be easily removed by
placing the BW switch in the Wide (up) position, energizing the NF mode.
If several heterodynes exist which are close together in frequency, it may
be necessary to advance the NIR control to eliminate them all, otherwise
the NF mode will eliminate them without help from the NIR mode. Note
that if the received voice level is reduced in the presence of a strong
heterodyne, the reduction in volume is caused by the receiver’s AGC, not
the NIR-10. Also note that if no heterodynes are present, the NF mode
may attack some of the voice frequencies, making the voice seem
somewhat distorted or “nasal”. If this is bothersome, merely disable the
NF mode by placing the BW switch in the lower (NARROW) position
until a heterodyne appears, then engage it.
PEAK MODE
on VOICE
The PEAK mode is designed to peak up any correlated information in the
audio passband. It provides a second type of noise reduction by
dynamically forming bandpass filters around correlated information,
thus automatically reducing the bandwidth to the minimum necessary to
pass the information. The PEAK mode is most effective on purely
random noise, such as white or pink noise. When more periodic noise
types are encountered, such as ignition noise or power line noise, the NIR
mode or a combination of NIR and PEAK modes may be more effective.
With the MODE switch in BYPASS, set the BW switch to the NARROW
(lower) position. This effectively bypasses the unit except for the internal
speaker driver. Now tune in a noisy sideband signal. Place the BW switch
in the middle (MED) position to enable the PEAK mode and notice the
reduction in the noise level. If desired, the NIR mode may also be enabled
19
and used in conjunction with the PEAK mode to provide additional
noise reduction.
NIR/PEAK MODE on
STATIC CRASHES
A static crash causes two problems which are annoying and disrupt
communications: First, a static crash of any reasonable duration is
offensive to the ears; Second, the receiver AGC is often driven to its limit
and requires a relatively long period of time to recover. During this
recovery period, the desired signal is momentarily “lost”. The NIR-10
can often provide significant reduction of the static impulse noise, and
manipulation of receiver characteristics can allow faster recovery of the
desired received signal. To counter the effects of a static crash, set the
NIR-10 in the NIR Mode and also in the PEAK mode. Adjust the NIT
control to about the 9:00 position (adjustment from this position may be
required later). Now change the receiver AGC characteristic from
SLOW to FAST. The NIR mode will reduce the long static crashes to
“pops” of about 130 millisecond duration, while the FAST AGC will
allow the receiver to recover rapidly. The result will be reasonably clear
audio with “pops” in the background.
NIR MODE on CW
While the NIR mode is designed to enhance speech, it will also perform
well on CW if the following limitations are observed: First, the CW note
should be in the range of 300 to 1000 Hz. Second, the CW speed must
not be too slow, or the unit will interpret it as an interfering tone and
attempt to remove it. In NIR mode, the unit should work well at speeds
above about 7 wpm. As with voice signals, adjust the NIR LEVEL
control until the noise is reduced and the CW still readable. The PEAK
function may also be used to reduce noise and enhance the CW signal
20
along with the NIR mode. NOTE: Turn off the NF mode when receiving
CW in the NIR mode. The notch will remove the tone from the CW
signal, making it impossible to copy.
NIR MODE on RTTY,
SSTV, PACKET, etc.
The NIR mode is designed to suppress these signals as they are considered
an interference to voice traffic. Use the BANDPASS mode for these
signals.
PEAK MODE on
CW/DATA
The PEAK mode is also quite useful on non-voice audio, such as CW,
RTTY, AMTOR, etc. Note that when using the PEAK mode with CW
signals, all tones existing in the audio passband are peaked, so if a signal
can be separated with the receiver filter, it can be further peaked and
noise-reduced using the PEAK function.
BANDPASS MODE
The BANDPASS mode is designed to enhance CW and DATA signals
(RTTY, SSTV, and Packet), and provide reduction in interference from
adjacent channel “chatter” on voice. When this mode is selected, the
NIR-10 becomes a bandpass filter with extremely steep skirts. The NIR
LEVEL control becomes the BP SHIFT control. Adjusting this control
will tune the filter to any frequency from 300 to 3400 Hz. The filter width
is selected by the BW switch and offers three options. Refer to the
Specifications in Section 6 for the exact bandwidths. When using
BANDPASS mode for CW, it’s best to start with the WIDE bandwidth
and narrow it down after you’ve tuned in the signal you’re interested in.
Adjust the filter frequency with the BP SHIFT control. Due to the
sharpness of the digital filter, it may be necessary to adjust the BP SHIFT
control slightly after changing the filter bandwidth. The signal will seem
21
to “pop” into the passband when properly tuned. If a “buzz” is heard,
particularly when in the NARROW bandwidth, it is caused either by not
having the received signal properly tuned in the center of the filter
passband, or by FM detection of audio harmonics, etc., on the vertical
skirts of the filter. Try carefully returning, or increase the bandwidth to
MED position to eliminate the “buzz”.
Narrow BW
Medium BW
Wide BW
Narrow bandwidth is most useful on CW; it may also be useful for
narrow-shift RTTY.
Medium bandwidth is useful for CW and RTTY.
Wide bandwidth is useful for CW, RTTY, SSTV, Packet and Voice.
BANDPASS MODE
on VOICE
Wide bandwidth is the only one useful for voice communications as
both the medium and narrow positions are too narrow for voice use. The
wide position is useful for eliminating high frequency “chatter” (adjacent
channel spillover) from the desired signal. Using the BP Shift control,
the bandwidth may actually be reduced below 1800 Hz to eliminate the
interference, while providing adequate intelligibility.
OPERATIONAL
LIMITATIONS
No physical device is perfect in its operation, and the NIR-10 is no
exception. The unit does have some operational limitations in both the
NIR and BANDPASS modes. We want you, the user, to be aware of the
limits to performance of the unit.
22
NIR Mode
Bandpass Mode
Notch Mode on CW
First, with the techniques used in the NIR-10, it is impossible to completely
recover speech when heavily corrupted by noise, because some of the
information that characterizes the speech is irretrievably lost. Because of
this, use of the NIR mode at signal-to-noise ratios of 0 dB and below may
actually reduce intelligibility rather than enhance it. Second, the noise left
over after reduction has an “electronic” sound. This is not an artifact
introduced by the processing as one might think, but rather it is all that
remains of the original input noise, which, because of its random nature,
cannot be removed completely. Unfortunately, this residual has also been
de-randomized to some extent, so that it occurs in bursts. Thus, it sounds
unnatural and can be more annoying than white noise. The higher the
level of noise in the input, the higher the level of this residual at the output.
One characteristic common to narrow steep-skirted filters, whether
analog or digital, is ringing. The NIR-10 has the digital equivalent of
ringing, which manifests itself as a “raspy” sound when an input signal
is placed on a band edge. Unlike analog filters, however, no ringing or
other disturbance of the signal occurs when it is placed in the passband.
Thus, it is usually possible to tune the NIR-10 so that the desired signal
is sufficiently far from the passband edges so that the raspy sound
doesn’t occur.
Remember to disengage the NOTCH filter by placing the BW switch in
the MED or NARROW positions or removal of the CW note will occur,
making CW operation impossible.
23
Peak Mode
TRANSMIT AUDIO
PROCESSING
The PEAK mode may not be effective at all on some types of impulse
noise. Use the NIR mode for these, or both NIR and PEAK together.
The noise reduction effectiveness of PEAK may also be degraded if the
audio input level from the receiver is too high. Merely reduce the receiver
volume and increase the NIR-10 VOLUME to compensate. Using both
the PEAK and NIR modes together will reduce or remove the electronic
artifacts and residual mentioned in the previous “NIR mode” paragraph.
The NIR-10 in NIR mode can also be used to process transmit audio.
The advantage is that background noise which may be picked up by your
microphone will be removed from your transmitted signal by the NIR
mode. This may be useful in a vehicle or other high ambient noise
environment.
Figure 4 on page 27 is a diagram of how this is might be accomplished.
A relay operated by the transmitter’s keyline output is used to switch the
NIR-10 input/output between transmit and receive. During receive, the
NIR-10 operates conventionally. During transmit, the NIR-10’s input is
fed from the amplified microphone source and its output is fed to the
transceiver’s transmit audio input. The microphone amplifier is necessary
since the unit hasn’t enough gain to operate on a low-level microphone
output directly. Some experimentation will be necessary to determine
usable operating levels in this configuration. Parts to implement this
circuit are available at Radio Shack or from your junk box.
24
SECTION 6
TECHNICAL
INFORMATION
SPECIFICATIONS
Audio Input
Frequency Response
Input Level
Absolute Output Delay
NIR and BP Modes
Bypass Mode
NIR Mode White Noise Reduction
MAX Control Position
MIN Control Position
PEAK Mode White Noise Reduction
NIR Mode Single Tone Reduction
MAX Control Position
MIN Control Position
Unbalanced 22Ω (or 47kΩ ). J3 is an RCA-type
phono jack)
300 to 3200 Hz +2 dB.
120 mV to 2.8 V rms. (Internal Level Select Jumper)
130 milliseconds.
<1 milliseconds.
Approximately 20 dB.
0 dB.
Typically 10 to 20 dB.
Greater than 40 dB.
0 dB.
Time to Cancel a Suddenly-Appearing Tone
NIR Mode:
About 250 milliseconds.
NF Mode:
About 3 milliseconds.
25
BP Mode Bandwidths
BP Mode Center Frequency
BP Mode Ultimate Rejection
NF Mode Ultimate Rejection
Normal Remote Bypass Input
Inverted Remote Bypass Input
Headphone Output
Speaker Output
Audio Output Distortion
Input Power
Size
Weight
Operating Temperature
Storage Temperature
Humidity
26
(Amateur) NAR: 250Hz, MED: 600 Hz, WIDE:
1800Hz (SWL) NAR:1800Hz, MED:2400Hz, WIDE:
3000Hz.
Continuously Variable in the 300Hz to 3200Hz range.
Greater than 60 dB.
Typically greater than 50 dB, one to four tones. Less
for more than four tones.
Forces Bypass Mode while driven to +3V or higher.
Forces Bypass Mode while pulled to +2V or lower.
Each has 10kΩ impedance and is protected to
+50V. (Phono Jacks)
For 8Ω and higher phones. (Stereo Phone Jack)
2W @ 10% dist. into an 8Ω Speaker. J2 is an RCAtype phono jack.
Less than 0.5% @ 1 kHz @ 0.5W Output.
+11 to +16VDC @ 1/2 A Avg., 1 A Peak
Reverse Polarity Protected. (2.5mm ID, 5 to
5.5mm OD coaxial jack).
2" x 7" x 6" (HxWxD)
2 lbs. (0.91 kg).
-20o C to +55oC.
-40o C to +85o C.
Up to 95% @ 55oC.
TROUBLESHOOTING
Symptom
Possible Fault
POWER ON LED does
not light.
Check AC power source and power line connection. Check for proper
seating of plug in the DC Power jack. Check polarity of DC Power: unit
will not operate (but will not be damaged) if polarity is wrong.
POWER LED is on, but
unit does not function and
PEAK LED does not flash
at power-up.
DC Input voltage is too low. Check adapter output voltage: it must be a
12V unit. Less likely: the unit has failed its self-test. Check PROMs U9
and U10 and processor U15 for proper seating. Turn off, then on. If fault
continues, contact JPS Customer Service.
Unit passes audio, but
won’t enter NIR or
BANDPASS mode.
Unit is held in BYPASS mode via remote control. Disconnect inputs to
J4 and J5; if problem clears, check your remote signal source for correct
operation. If problem does not clear, contact JPS.
PEAK LED is on almost
continuously.
Input audio level is excessive. Reduce your input level until the indicator
flashes occasionally on voice peaks.
PEAK LED flashes at
power-up but never lights
otherwise.
Input audio level is too low for best NIR-10 performance. If your level
cannot be raised, increase the gain of the NIR-10. See Section 3 on Input
Level Adjust.
Audio at phones but not
at speaker.
Check your speaker and speaker connection.
Audio at speaker but not
at phones.
Check your headphones and connections. Also if you are using mono
phones, see Section 4 regarding the headphone output.
27
REMOTE BYPASS
CONNECTIONS
This section offers some guidance on hooking up the NIR-10’s remote
bypass inputs to your transmitter or transceiver. Since there are so many
types of radios in existence, it is impossible for us to give specific
instructions for interfacing to every radio. For this reason, we have
designed the NIR-10 to be as easy to interface as possible.
NOTE
You need to use these remote bypass connections only if you
intend to monitor your own transmission (sidetone) through
the NIR-10. If you don’t need this feature, you may ignore this
section.
28
General Principle
The general principle of the installation is to put the NIR-10 into
BYPASS mode whenever your transmitter is keyed. This will remove
all processing plus the input to output delay to allow you to monitor your
own transmission through the unit. To do this, you must connect one
of the NIR-10’s REMOTE BYPASS inputs to a signal from your
transmitter that tells when your transmitter is keyed.
Connect to your
Transceiver's
Remote Connector
Most recent commercial transceivers have a remote or accessory connector
which contains a signal intended to key a linear amplifier. (Consult your
transceiver’s instruction manual for the pin number and characteristics.)
This is the signal to use to drive the NIR-10. Normally, this signal is a
contact closure to ground when keyed. If this is the case, use the INVert
REMOTE BYPASS (J5) connector. This connector has a built-in pull-
up resistor, so a shielded cable is all that’s needed. (Always use a shielded
cable for these interconnections.)
If the Signal
is already in use
If this keying signal is already in use on your system (keying an amplifier
or some other use), you can generally tie the invert BYPASS INPUT to
it anyway without ill effects. The J5 input is high impedance (10kΩ) so
that it won’t load your output and will withstand high voltages (+50V)
without damage.
If your Transceiver
has no Remote
Connector
If your transceiver does not have a remote connector or remote key
output, you can probably connect the NIR-10 in parallel with your
microphone’s PTT switch or CW key. Caution: if your transceiver is a
tube type, make certain that the keying voltage is positive and less than
50V. Again, having the NIR-10 input connected will probably cause no
ill effects, because the input impedance is so high. Normally, these
switches are contact closures to ground so they’ll also connect to the
INVert REMOTE BYPASS (J5) input.
Using the REMOTE
BYPASS Input
Most transceivers require a contact closure to ground to key them and
they supply a contact closure to ground (or equivalent) as an output. If,
instead, your transceiver sources a positive logic voltage when keyed,
then connect this signal to the REMOTE BYPASS input (J4). This input
is also high impedance and will withstand +50V.
Do NOT connect to
the Antenna
The NIR-10’s REMOTE BYPASS inputs are designed to be operated by
a DC logic signal only, not RF. Therefore, DO NOT connect either of
these inputs to the ANTENNA output of your transmitter. The NIR-10
29
will be damaged and your transmitter output may be damaged as well.
AUDIO SECTION
TECHNICAL
DESCRIPTION
30
The Audio Circuitry is detailed in Figure 2. The diagram is a full
schematic of the audio and power supply and includes all circuitry which
is not DSP hardware. The full schematic is given here because we
consider it possible to troubleshoot these sections of the circuitry in the
field.
Audio Input
Audio input at connector J3 is routed to op-amp U18A, a unity-gain
buffer amplifier. Resistors R33 and R32 along with diodes CR8 and
CR9 protect U18A against input overloads. Op-amp U18B is a variablegain amplifier that provides the audio input to the DSP section. Jumper
JP2 sets the gain range to allow the NIR-10 to function at input audio
levels between 120mV and 2.8V.
Audio Output
The processed audio signal from the DSP circuitry is fed to the volume
control pot R14. The input to speaker driver IC U19 is the signal from
the wiper of the front panel volume pot. U19 drives the stereo headphone
jack through rfi filter L1-C18. The speaker output J2 is passed through
the headphone jack, so that it is disabled whenever headphones are
plugged in.
Miscellaneous
Gates U16A and U16B and associated components condition the remote
bypass inputs. Serial resistors R9 and R10 along with diodes CR1
through CR4 protect the gate inputs against overloads. The output of
U16A feeds the DSP parallel input port where its state is read by the
processor. The mode select and bandwidth select switches are also fed
to the DSP input port to be read by the DSP. Noise in the input, the higher
the level of this residual at the output.
Power Supply
DSP SECTION
TECHNICAL
DESCRIPTION
The power supply includes U20, a passive 5V regulator, and U17, a
switched-capacitor voltage converter. The DC voltage at J1 is applied
through power switch SW3. Series diode CR5 protects against reversed
polarity. A filter made up of C18, C19, and L4 suppresses trash that might
be radiated by the power leads. U17 furnishes the -5V required by the A/
D converter and the op-amps.
The +5V is generated by regulator U20. Series resistor R25 limits U20’s
dissipation.
Figure 3 is a simplified schematic of the DSP section of the NIR-10. Only
a simplified schematic is presented because this section is virtually
impossible to troubleshoot without specialized equipment.
The general purpose of the DSP hardware is to convert analog signals to
the digital domain, operate on and manipulate these signals digitally using
the DSP chip, then convert the result back to analog. In the digital
domain, the main tasks are to differentiate any speech components from
the rest of the incoming signal (NIR mode) and band limit the signal
(BANDPASS mode).
DSP and AIC
The heart of the DSP section is U15, a TMS320C25 DSP chip which
performs all DSP functions other than A to D and D to A conversion. The
chip runs at 40 MHz which is supplied by clock oscillator U7. U13 is a 14-
31
bit Analog to Digital and Digital to Analog Converter. It provides the
interface between the analog and digital realms. It supplies to, and
accepts from, the DSP chip a serial digital expression of the input and
output analog waveforms.
32
Reset Generator
U103 is a reset generator which ensures an orderly power-up sequence
for the DSP and associated components. It senses the voltage on the
+5V line and generates a reset while the voltage is below approximately
4.55V. As the voltage rises above the threshold, a delay is generated to
ensure processor clock stability before operation commences.
Memory
EPROMS U9 and U10 provide program storage and static RAMs U11
and U12 provide data storage for the program.
Software
Noisy speech is speech that has been corrupted by some type of noise,
such as “white” noise, electrical impulse noise, or acoustic noise.
Enhancement of noisy speech generally implies that all the noise is
removed while the speech remains intact. In practice it’s not quite this
simple, since speech which has been corrupted by noise has irretrievably
lost some of its original characteristics. Complete removal of all noise
components may sometimes result in speech which is harder to listen to
and interpret than the same speech passage with some particular noise
components retained. There is a trade-off between intelligibility (can
one determine what is being said?) and “listenability” (how pleasing...or
grating...is the monitored audio?). Maximum noise component removal
may turn an irritating noisy and tone-overlaid signal into one that’s
much more pleasing to the ear, but the received speech must be
understood as well. The aim of noise reduction in speech is to improve
not only the listenability of the noisy speech, but to improve its intelligibility
as well. Noisy speech is difficult to listen to, since the brain has to work
hard to discriminate between speech and noise. For this reason, fatigue
may result when an operator attempts to interpret noisy speech for
extended periods. There are times when intelligibility is more important
than the pleasantness of the signal, while at other times the emphasis is
placed on the listenability.
The NIR-10 software offers continuously variable noise reduction
adjustable with the front panel NIR LEVEL control. The voltage set by
the arm of the pot is digitized by its own A/D converter, U6. This allows
the operator to choose the best balance between intelligibility and
listenability. The proper setting of the NIR LEVEL control will be
determined mainly by the type of noise and the signal to noise ratio of the
noisy speech. In general, signals with low signal to noise ratios (i.e. 0dB
or less) will work best at the minimum setting, while stronger, cleaner
signals will benefit from more reduction.
Peak Detector
A peak detector monitors the input audio and flashes the Peak LED on
audio peaks which are still somewhat below saturation. This function
aids in setting up the NIR-10 with the proper audio levels.
33
34
FIGURE 2 NIR-10 Audio and Power Supply Section Schematic
FIGURE 3 NIR-10 DSP Section Schematic
35
FIGURE 4 Connections for Transmit Audio Processing
36